relative is an angular directive which parses its element's
text-content or datetime attribute and replaces the contents with a
time relative to now, e.g., "1 day ago" instead of a fixed date or
"in 87 years" instead of "2100".

It also sets the element's title attribute to a nicely formatted
time localized to the browser's timezone so people can hover to get
the original datetime.

Every directive instance sets up a timeout. The timeouts are however
set up in a way that they fire only when it makes sense, as in, they
fire when the text rendered by Moment.js would actually change, not
before and not after.